Mg-Zn-Sn계 합금 압출 및 압연재의 미세 조직과 기계적 특성 평가

Abstract

Magnesium alloys have attracted significant interest due to their high potentially lightweight materials for structural applications such as automotive and aerospace industry. However, application of magnesium alloys is limited to components because of low mechanical properties and poor corrosion resistance at elevated temperature. Magnesium alloys that derive their strength from precipitation hardening are usually considered the most promising for such applications and the thermal stability of the precipitate distribution is an important component of the overall microstructural stability. However, precipitation hardening in magnesium alloys is still rather poorly explored and insufficiently developed area. Zn is a promising candidate which has several benefits in Mg-based alloys. Zn increases the creep resistance, and forms several stable intermetallic phases with Magnesium. Mg-Zn alloys is one of the most promising alloys which have moderate strength and corrosion resistance due to formation of metastable phase such as MgZn, MgZn2 and Mg2Zn3. The motivation for adding Sn is the expected precipitation of Mg2Sn, which is belived to be stable at elevated temperature, and like Zn, Sn has a strong potential for precipitation hardening of Magnesium. In this reserch, Mg-Zn-Sn alloys cast by changing the Mn, Zn content for improve strength and elongation, we estimated hot extrusion and hot rolling properties the effect of Mn, Zn addition. In addition, we investigated microstructure and mechanical properties of as-cast, as-extruded and as-rolled materials effect of Mn, Zn was addition. In the Mg-3Zn-2Sn as-extruded alloys, with increasing Mn addtions, grain size was decreased. ultimate tensile strength and elongation increse. Especially, in the case of Mg-3Zn-2Sn-0.4Mn, elongation was obtained 39%. In the Mg-xZn-2Sn hot rolled alloys, with Zn additions increase, volume fraction of second phase were increased. MgZn and Mg2Sn phase were major the second phase. With the increase of Zn content, volume fraction of Zn eutetic phase are increased. And MgZn phase are located at the dendrite grainboundary. It is indicated that the Mg matrix is easier to form by themodynamic solidification interpretation at solidification than MgZn eutetic phase. And with Zn additions, ultimate tensile strength was increased. but elongation was decreased. In the Mg-xZn-2Sn hot-rolled alloys, with increasing 0.4 wt% Mn addtions, grain size was decreased 23㎛ to 7.1㎛. Also, ultimate tensile strength and elongation was incresed. Especially, in the case of Mg-10Zn-2Sn-0.4Mn alloy after annealing during 30min at 573 K of Mg-10Zn-2Sn alloy, yield strength and ultimate strength was obtained 229 MPa and 340MPa respectively. And elongation was obtained 20%.

Key word : Mg-Zn-Sn alloy, hot extrusion, hot rolling, microstructure, mechanical property